T 2.3.5.5

But custom not only gives a facility to perform any action, but likewise an inclination and tendency towards it, where it is not entirely disagreeable, and can never be the object of inclination. And this is the reason why custom encreases all active habits, but diminishes passive, according to the observation of a late eminent philosopher. The facility takes off from the force of the passive habits by rendering the motion of the spirits faint and languid. But as in the active, the spirits are sufficiently supported of themselves, the tendency of the mind gives them new force, and bends them more strongly to the action.